A significant drawback of most lasers is that they are tunable, at most, over a very limited wavelength range. This drawback is overcome to some extent by optical parametric oscillator systems which are used to generate secondary (parametrically generated) radiation from monochromatic coherent primary radiation by means of parametric interaction with an optically nonlinear medium. In the optical parametric process, primary incident radiation having a known frequency propagates through a nonlinear medium and is converted into secondary radiation at two lower frequencies (longer wavelengths). The secondary or parametric radiation has two components, typically referred to as a signal wavelength and an idler wavelength. The secondary components can be adjusted in wavelength by a suitable tuning arrangement, typically by rotation of the optically nonlinear medium within the optical resonator of the parametric system. The optical parametric system can be used in combination with a coherent source of primary optical radiation such as a laser to provide a source of optical radiation whose wavelength can be varied within a prescribed frequency range.
A tunable optical system including a laser and a separate optical parametric oscillator is relatively complex and expensive. In the optical parametric oscillator, the nonlinear medium is typically located within an optical resonator formed by mirrors so that the radiation passes repeatedly through the nonlinear medium. Since laser radiation must be coupled into the optical resonator, mirrors which are highly transmissive for the primary laser radiation and highly reflective for the secondary parametric radiation must be used. This requirement is difficult to meet when the wavelength of the secondary radiation is to be continuously tunable, since the mirrors must be highly reflective at a wavelength that is close to the wavelength of the primary radiation. The mirrors should exhibit high reflectivity over a wide range of wavelengths. Even the most highly developed dichroic mirrors made of multiple dielectric layers only partially meet this requirement and then at great cost.
A triply resonant optical parametric oscillator is described by W. Brunner et al in "Theory of Optical Parametric Amplification and Oscillation", Progress in Optics, Vol. XV, North-Holland, 1977, pp. 44-49. An internally Q-switched, solid state laser is described by Cordova-Plaza et al in IEEE Journal of Quantum Electronics, Vol. QE-23, No. 2, February 1987, pp. 262-266.
It is a general object of the present invention to provide optical parametric oscillator/laser systems.
It is another object of the present invention to provide a tunable source of coherent optical radiation.
It is a further object of the present invention to provide an optical source wherein laser radiation and optical parametric radiation are generated in an embedded dual optical resonator.
It is a further object of the present invention to provide an optical source wherein laser radiation and optical parametric radiation are generated within a single nonlinear optical medium.
It is another object of the present invention to provide a triply resonant optical parametric oscillator/laser system.